Charge Separation of Dense Two-Dimensional Electron-Hole Gases: Mechanism for Exciton Ring Pattern Formation

(Received 29 August 2003; published 18 March 2004)We report on new experiments and theory that unambiguously resolve the recent puzzling observa-tion of large diameter exciton emission halos around a laser excitation spot in two dimensional systems.We find a novel separation of plasmas of opposite charge with emission from the sharp circularboundary between these two regions. This charge separation allows for cooling of initially hot opticallygenerated carriers as they dwell in the charge reservoirs for very long times.